1. Field of the Invention
The present invention relates to a process for producing fluorine-containing aliphatic carboxylic acids. More particularly, this invention provides a convenient and effective process for producing the mentioned acids from fluorine-containing aliphatic halogen compounds as starting material. Fluorine-containing aliphatic carboxylic mono- and di-carboxylic acids are useful from their chemical and physiological properties particularly as surfactant, water and oil repellent agent, medicine, agricultural chemical, and the synthetic intermediates thereof. Furthermore, they are useful materials for industrial applications as monomer for producing fluorine-containing polymers of various kinds, such as, for example, for paint materials and for resists employed in the production of LSI's, etc.
2. Description of Prior Arts
Conventional processes of synthesizing fluorine-containing aliphatic carboxylic acids are roughly classified into two groups. One group involves the electrolytic fluorination of aliphatic halogen compounds, and the other starts from a fluorine-containing aliphatic halogen compound.
Among them, processes which utilize the reaction of fluorine-containing aliphatic halogen compounds with carbon dioxide in the presence of metal is known to be relatively readily accessible. They include processes using lithium or magnesium as disclosed in J. Am. Chem. Soc., 73, 3158 (1951); J. Fluorine Chem., 4, 247 (1974); J. Org. Chem., 33, 280 (1967) and Chem. Abs., 53, 6987g: also included is a process which employs zinc alone or a metal couple of zinc and other metal as described in Japanese Laid-Open Patent Application No. Sho 53-77008. Further, a process has been proposed in which the reaction is carried out with zinc powder under the influence of ultrasonic wave. Furthermore, a process in which a fluorine-containing aliphatic halogen compound is made to react with carbon monoxide in the presence of palladium.
However, these processes mentioned above do not suffice to be satisfactorily employed in industry. In the process using magnesium or lithium, the fluorine-containing organic compound produced as intermediate is very unstable and therefore the reaction should be carried out at a low temperature, say -100.degree. or -40.degree. C., and the carboxylic acid can be obtained only with a low yield.
With the processes using zinc metal, a very low yield is expected when zinc is used alone. When zinc is used together with another metal to form a metal couple, the conversion rate of the raw material as well as the yield of carboxylic acid aimed at are improved, but the yield itself is still too low to attain an efficient process for commercial production. In addition, the metal couple of zinc and other metal should be prepared in advance, and it is difficult to operate the process with a high reproducibility and therefore a constant reproducible yield is difficult to obtain.
With the process in which ultrasonic wave is irradiated in the presence of zinc powder, a high power ultrasonic wave generator is difficult to obtain and a low yield is expected. Therefore it is not an effective process from the point of industrial processes. In the process which involves carbon monoxide using palladium as catalyst, the expense of palladium catalyst and the high toxicity of carbon monoxide prevent the process from being advantageously used as an industrial synthetic method.
As has been mentioned above, the conventional processes directed to the production of fluorine-containing aliphatic carboxylic acids starting from fluorine-containing aliphatic halogen compounds suffer from the following problems:
(1) reaction conditions are difficult to set up;
(2) yield is low; and
(3) reaction is complicated to operate.